1. Technical Field
The present invention relates to methods of growing group III nitride crystals by a liquid-phase technique, and to group III nitride crystals produced by the growth methods.
2. Description of the Related Art
Group III nitride crystals are widely employed as wafers or similar substrates for various semiconductor devices. Bulk group III nitride crystals have been sought in recent years for the sake of manufacturing the various semiconductor devices efficiently.
Methods of growing group III nitride crystals include vapor-phase techniques such as hydride vapor phase epitaxy (HVPE) and metalorganic chemical vapor deposition (MOCVD), and liquid-phase techniques such as high-pressure solution growth and flux growth. Compared with vapor-phase techniques, liquid-phase techniques are superior from an environmental protection aspect, because toxic gases are not employed in the crystal growth.
For example, M. Bockowski, “Growth and Doping of GaN and AlN Single Crystals under High Nitrogen Pressure,” Crystal Research &Technology, Vol. 36, Issue 8-10, 2001, pp. 771-787 (Non-patent Document 1) discloses, as a method of growing group III nitride crystal by a liquid-phase technique, a GaN crystal growth method by high-pressure solution growth. Likewise, H. Yamane, et al., “Preparation of GaN Single Crystals Using a Na Flux,” Chemistry of Materials, Vol. 9, No. 2, 1997, pp. 413-416 (Non-patent Document 2) discloses a method of growing GaN crystal by an Na-flux technique. Additionally, Japanese Unexamined Pat. App. Pub. No. 2003-206198 (Patent Document 1) discloses a method of growing GaN crystal by an Na-flux technique, employing platelike group III nitride seed crystals.
Owing to its crystal-growth conditions being a high 1 GPa in pressure and a high 1500° C. in temperature, the growth method disclosed in the Crystal Research &Technology article (Non-patent Document 1) raises the crystal manufacturing costs, and the fact that the method does not employ seed crystals is prohibitive of growing bulk crystal. Meanwhile, although the crystal-growth conditions for the growth method disclosed in the Chemistry of Materials article (Non-patent Document 2) are, at 800° C. and 10 Mpa, relatively easy to implement, because seed crystals are not employed in that case as well, growing bulk crystal is challenging. Furthermore with regard to the growth method disclosed in the Crystal Research & Technology article (Patent Document 1), inasmuch as the diametric span of the platelike seed crystal that is employed is not large, bulk crystal cannot be obtained.
As mentioned earlier, group III nitride crystal can be grown by liquid-phase methods such as high-pressure solution growth and flux techniques. For example, onto a platelike group III nitride seed-crystal substrate of large diametric span, a group III nitride crystal having the same chemical composition as the substrate can be homoepitaxially grown. With this procedure, nevertheless, cracking occurs in the substrate and in the group III nitride crystal grown onto the substrate, which is prohibitive of producing bulk group III nitride crystal substrates.